Power Quality

Types of Power Quality Problems

Power quality disturbances range from surges that last only microseconds to outages that continue for hours. Some common examples include the following:

Temporary Interruption

Description: Planned or accidental total loss of power in a localized area of community
Duration: From 2 seconds to 2 minutes
Causes: Equipment failure, weather, animals, human error (auto accidents, kites, etc.)
Effect: Systems shut down
Possible Solutions: Uninterruptible power supply, uninterruptible power supply with generator

Long-Term Outage

Description: Planned or accidental total loss of power in a localized area of community
Duration: Over 2 minutes
Causes: Equipment failure, weather, animals, human error (auto accidents, kites, etc.)
Effect: Systems shut down
Possible Solutions: Uninterruptible power supply, uninterruptible power supply with generator

Momentary Interruption

Description: Very short planned or accidental power loss
Duration: Milliseconds to second or two
Causes: Switching operations attempting to isolate an electrical problem and maintain power to your area
Effect: Equipment trips off, programming is lost, or disc drive crashes
Possible Solutions: Uninterruptible power supply, motor generator, standby power supply

Sag or Undervoltage

Description: A decrease in voltage
Duration: Milliseconds to a few seconds, undervoltages are sags that are longer than a few seconds
Causes: Major equipment start-up or shutdown, short circuits (fault clearing), undersized electrical circuit
Effect: Memory loss or data errors, dim or bright lights, shrinking display screens, equipment shutdown/reset
Possible Solutions: Relocate computer to a different electrical circuit, voltage regulator, constant voltage transformer (Ferro-resonant transformer), power conditioner, uninterruptible power supply, motor generator, capacitor/flywheel/superconductor storage

Swell or Overvoltage

Description: An increase in voltage
Duration: Milliseconds to a few seconds, overvoltages are swells that are longer than a few seconds
Causes: Major equipment start-up or shutdown, short circuits (fault clearing), undersized electrical circuit
Effect: Memory loss or data errors, dim or bright lights, shrinking display screens, equipment shutdown
Possible Solutions: Relocate computer to a different electrical circuit, voltage regulator, power conditioner, uninterruptible power supply, motor generator

Transient, Impulse, or Spike

Description: A sudden change in voltage up to several hundred to thousand volts.
Duration: Microseconds
Causes: Utility switching operations, starting and stopping equipment or machinery, static discharges, lightning
Effect: Processing errors, data loss, burned circuit boards
Possible Solutions: Surge suppressor (for transients), power conditioner, motor generator

Notch

Description: A disturbance of opposite polarity from the waveform
Duration: Microseconds
Causes: Utility switching operations, starting and stopping equipment or machinery, static discharges, lightning
Effect: Processing errors, data loss, burned circuit boards
Possible Solutions: Surge suppressor (for transients), power conditioner, motor generator

Noise

Description: An unwanted electrical signal of high frequency from other equipment
Duration: Sporadic
Causes: Electromagnetic interference: from appliances, microwave and radar transmissions; from radio and TV broadcasts, arc welding, heaters; from laser printers, thermostats, loose wiring; or from improper grounding.
Effect: Disturbs sensitive electronic equipment, but is usually not destructive. It can cause processing errors and data loss.
Possible Solutions: Isolation transformer, power conditioner, uninterruptible power supply, motor generator

Harmonic Distortion

Description: An alteration of the pure sine wave (sine wave distortion), due to non-linear loads, on the power supply
Duration: Sporadic
Causes: Non-linear loads
Effect: Causes motors, transformers and wiring to overheat
Possible Solutions: Electrically separate non-linear loads and wire per Appendix A to limit harmonic distortion